We have estimated the adenosine triphosphate (ATP) as an expression of the viable mass of dental plaque from monkeys and have succeeded in expressing this mass as equivalent cell numbers of Streptococcus sanguis. Our estimates of the number of viable cells per unit mass of plaque is comparable to those reported by other using conventional microbiological methods. Very small plaque samples obtained from individual teeth could be analyzed for viable cell mass by ATP content and total cell mass by protein estimation. We have started studies of other methods to use for the normalization of plaque samples in terms of total cell mass. Flavin mononucleotide and iron porphyrin compounds can be detected in the same plaque extracts for which we have estimated the ATP content. We are presently testing the possibilities of using one of these constituents as an estimate of total plaque mass to overcome the limitations of using protein content. Work is continuing on the analysis of volatile fatty acids to examine the fermentation products of dental plaque. In addition, studies are proceeding to calculate the energetic contribution of the sugar moieties found in saliva to the growth of bacteria found in dental plaque.